The maximum number of Amazon EBS volumes that you can attach to an instance depends on the instance type and instance size. When considering how many volumes to attach to your instance, you should consider whether you need increased I/O bandwidth or increased storage capacity.
Bandwidth versus capacity
For consistent and predictable bandwidth use cases, use Amazon EBS-optimized instances with General Purpose SSD volumes or Provisioned IOPS SSD volumes. For maximum performance, match the IOPS you have provisioned for your volumes with the bandwidth available for your instance type.
For RAID configurations, you might find that arrays larger than 8 volumes have diminished performance returns due to increased I/O overhead. Test your individual application performance and tune it as required.
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Volume limits for instances built on the Nitro
System
The volume limits for instances built on the Nitro System depend on the instance type. Some Nitro instance types have a dedicated EBS volume limit, while most have a shared volume limit. To view the volume attachement limits for each instance type, see the following:
Dedicated EBS volume limit
The following Nitro instance types have a dedicated EBS volume limit that varies depending on instance size. The limit is not shared with other device attachments. In other words, you can attach any number of EBS volumes up to the volume attachment limit, regardless of the number of attached devices, such as NVMe instance store volumes and network interfaces.
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General purpose: M7a | M7i | M7i-flex | M8g
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Compute optimized: C7a | C7i | C7i-flex | C8g
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Memory optimized: R7a | R7i | R7iz | R8g | U7i-6tb | U7i-8tb | U7i-12tb | U7in-16tb | U7in-24tb | U7in-32tb | U7inh-32tb | X8g
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Storage optimized: I7ie | I8g
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Accelerated computing: F2 | G6 | G6e | Gr6 | P5 | P5e | P5en | Trn2 | Trn2u
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High performance computing: Hpc7a
Shared EBS volume limit
All other Nitro instance types (not listed in Dedicated EBS volume limit) have a volume attachment limit that is shared between Amazon EBS volumes, network interfaces, and NVMe instance store volumes. You can attach any number of Amazon EBS volumes up to that limit, less the number of attached network interfaces and NVMe instance store volumes. Keep in mind that every instance must have at least one network interface, and that NVMe instance store volumes are automatically attached at launch.
Most Nitro instances support a maximum of 28 attachments. The following examples demonstrate how to calculate how many EBS volumes you can attach.
Examples
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With an
m5.xlargeinstance with only the primary network interface, you can attach 27 EBS volumes.28 volumes - 1 network interface = 27
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With an
m5.xlargeinstance with two additional network interfaces, you can attach 25 EBS volumes.28 volumes - 3 network interfaces = 25
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With an
m5d.xlargeinstance with two additional network interfaces, you can attach 24 EBS volumes.28 volumes - 3 network interfaces - 1 NVMe instance store volume = 24
Volume limits for Xen-based instances
The volume limits for Xen-based instances, such as T2, depend on the operating system.
For more information, see Xen-based instances.
Linux instances
Attaching more than 40 volumes to a Xen-based Linux instance can cause boot failures. This number includes the root volume, plus any attached instance store volumes and Amazon EBS volumes.
If you experience boot problems on an instance with a large number of volumes, stop the instance, detach any volumes that are not essential to the boot process, start the instance, and then reattach the volumes after the instance is running.
Important
Attaching more than 40 volumes to a Xen-based Linux instance is supported on a best effort basis only and is not guaranteed.
Windows instances
The following table shows the volume limits for Xen-based Windows instances based on the driver used. That these numbers include the root volume, plus any attached instance store volumes and Amazon EBS volumes.
| Driver | Volume Limit |
|---|---|
|
AWS PV |
26 |
|
Citrix PV |
26 |
|
Red Hat PV |
17 |
We recommend that you do not that attach more than 26 volumes to a Xen-based Windows instance with AWS PV or Citrix PV drivers, as it is likely to cause performance issues. To determine which PV drivers your instance is using, or to upgrade your Windows instance from Red Hat to Citrix PV drivers, see Upgrade PV drivers on EC2 Windows instances.
Important
Attaching more than the following number of volumes to a Xen-based Windows instance is supported on a best effort basis only and is not guaranteed.
For more information about how device names are related to volumes, see How volumes are attached and mapped for Amazon EC2 Windows instances.
